The invention relates to a safety clutch for rotating drives having
a driving and a driven hub which are mounted for rotation in relation to one another,
two locking arrangements each of which is connected to one of the hubs for joint rotation,
at least one detent member which, in an engaged position, couples the two locking arrangements to one another and produces an axial disengaging force depending on the transmitted torque, and
a loading device to produce an engaging force which can be overcome by the disengaging force if a specific torque is exceeded.
In a known safety clutch of this type (Brochure No. 8312 I.A of Messrs. Fertigungstechnik Walter Hafner, D-8751 Kleinwallstadt, page 14, series FHW/BA), the two hubs have annular end faces which lie in a common plane and comprise detents which extend radially with respect to the axis of rotation of the clutch. Cylindrical rolling bodies are provided as detent members, which rolling bodies are likewise arranged radially and are loaded axially by a loading device in the direction of the detents.
The loading device includes a ring on which the detent members can roll and which is prestressed by a cup spring. The prestressing can be adjusted by a nut which is screwed onto one of the two hubs and against which the cup spring is supported. The same hub has to be secured directly to a driving shaft while the other hub is secured to a driven shaft selectively directly or through a resilient corrugated tube.
In another safety clutch of the said type which is likewise known (Brochure of Messrs. Binder & Geisser AG, CH-8029 Zurich, series SIK-ZF), balls are provided as detent members instead of cylindrical rollers.
In further known safety clutches of the said type (Brochure of the Maschinenfabrik Monninghoff GmbH & Co. KG, D-4630 Bochum) the locking arrangements are crown gears which are also known by the name of Hirth toothing; here the teeth of each of the two sets of crown toothing represent detent members which engage in the gaps between the teeth in the other set of toothing. An electromagnet with associated armature is provided as a loading device which tends to hold the two sets of crown teeth together.
It is common to all these known safety clutches that the detent members slip over the locking arrangement or arrangements in which they normally engage, if a certain torque is exceeded. The magnitude of this torque depends on the formation of the locking arrangements, for example on the tooth flank angle if the locking arrangements are crown teeth, and further depends on the axial engaging force which is produced by the loading device.
When the detent members slip over the locking arrangement or arrangements, a torque, which is not negligible, is still transmitted; in addition, the detent members and locking arrangements wear away to a considerable degree if the slipping continues for a long time. This can possibly be counteracted in electromagnetic clutches as a result of the fact that their supply of current is cut off if the detent members leave their normal position. Because of the inevitably large inert masses of their windings and armatures, electromagnetic clutches are not, however, suitable for applications in which it is important to keep the rotating inert masses small.
It is therefore the object of the invention to develop further a safety clutch for rotating drives in such a manner that when a certain torque, which is still regarded as permissible, is exceeded, it still transmits only a very slight residual torque in comparison with this torque and wherein the inert masses rotating with each of the two hubs are small in comparison with electromagnetic clutches of the same capacity.
According to the invention, the problem is solved in that
the loading device comprises a cylinder compartment to which a fluid under pressure can be supplied from an inlet so long as the detent member is engaged, and
the detent member is connected to a distributing slide valve for joint axial displacement, which slide valve separates the cylinder compartment from the inlet and connects it to a relief passage if the detent member is at least partially disengaged.
Compressed air may be used as fluid for producing the engaging force, which has the advantage that the filling of the cylinder compartment has a negligibly small inert mass; in addition, the compressibility of the air facilitates the initial movement of the distributing slide valve, which is necessary during the disengagement.